1. Field of the Invention
This invention relates to the detoxification, reduction or removal of organic pollutants from fluids such as water or air. Such pollutants include trihalomethanes, polychlorinated biphenyls (PCBs), pesticides, benzene derivatives and others.
2. Description of the Prior Art
For some time it has been known that, in the presence of certain wavelengths of light, titanium dioxide and certain other semiconductors can achieve photodechlorination of PCBs. U.S. Pat. No. 4,892,712 (Robertson et al) summarizes the prior art, referring to publications by Carey et al, Chen-Yung Hsiao et al, Matthews, and Serpone et al.
The Matthews apparatus contained a coil around a lamp, where transparent glass tubing was used to form a single, continuous, self-contained fluid channel. In this configuration, the tubing must be transparent in order for the photoactive coating inside the tube to receive the light. Also, more than 50% of the light generated by the lamp is lost between the spaces of each revolution of the coils and the walls of the tubing. This type of assembly would not be practical in a commercial application.
The invention in the Robertson et al patent attempts to "adapt [the] previously observed laboratory reaction to a practical fluid purification system . . . ". Robertson et al recognized that in order for the process to be practical, the TiO.sub.2 must be immobilized to some substrate. They accordingly immobilized a TiO.sub.2 coating on a porous, filamentous, fibrous or stranded, transparent matrix such as a fiberglass mesh, through which the fluid can flow in intimate contact with the photoreactive material. The matrix, e.g. fiberglass mesh, is wrapped in several layers around a fluorescent lamp. The matrix must be sufficiently transparent for light to penetrate to the outer layers of the mesh. Accordingly, either a transparent base material such as glass must be used or a matrix with a sufficiently open structural form, such as a screen, must be used, so that light can penetrate to the outer layers.
The use of concentric layers of transparent substrates, treated with the photoactive materials, is limited by the ability of the light to penetrate successive layers. The requirement that the substrate material be substantially transparent and inert to the reactants further limits the choice of substrates.
In all of the prior art, either the TiO.sub.2 (or other semiconductor) must be in suspension in the fluid in transparent tubing, or the substrates to which the semiconductor is bound must be transparent to light, in order for the photoactive materials to be exposed.